Ink-jet recording methods have been practiced in which recording is carried out by ejecting colorant containing ink droplets from ejection orifices. It is required that inks which are employed for ink-jet recording can preferably be printed onto plain paper (for example, PPC paper such as electrophotographic paper and recording paper commonly employed for general business use such as continuous paper sheets for computers.
However, when plain paper is employed, irregular bleeding (feathering) of image edges tends to occur resulting in degradation of printing quality. In order to minimize such feathering, one known method is to lower the surface tension by addition of solvents such as polyhydric alcohols (for example, 1,2-hexanediol), or alkyl ethers (for example, triethylene glycol monobutyl ether). When polyhydric alcohols or alkyl ethers are incorporated to achieve the desired improvements, problems tend to occur in which fine lines are broadened (bleeding), and ink penetrates to the reverse side of plain paper (reverse side penetration), whereby it is not possible to achieve the desired image density. Further, when ink excessively penetrates to the reverse side, problems occur in which it is not possible to record both sides of plain paper by the use of ink-jet printing.
Further, it has been demanded to minimize the generation of mottling (beading) in solid image printed portions. Problems of mixing between colors (bleeding) remains unsolved.
In order to overcome these image quality problems related to plain paper, methods are reported (refer, for example, to Patent Documents 1 and 2) in which polysaccharides or specific surface active agents are added to ink. Further, reported is a method (refer, for example, to Patent Document 3) in which a liquid composition comprising a cationic substance is allowed to react with an ink comprising an anionic substance on the medium to be recorded; a method (refer, for example, to Patent Document 4) in which ink penetration is controlled employing a heater; and a method (refer, for example, to Patent Document 5) in which an image is formed on a transfer body and the resulting image is transferred to a recording medium. However, these methods, in turn, result in problems of storage stability as well as problems in which the apparatus becomes over-sized.
Further, ink-jet printers are required to achieve performance which not only results in high image quality but also stably ejects ink over an extended period of time. The aforesaid performance occasionally depends on the structure of colorants. However, detailed investigation has not been performed and these problems have not yet been overcome. As noted above, based on conventional techniques, it is possible to find means in which specific performance is independently improved. However, no inks have been prepared which simultaneously meet the required performance and solve the series of problems.
(Patent Document 1) Japanese Patent Publication Open to Public Inspection (hereinafter referred to as JP-A) No. 6-228477 (claims)
(Patent Document 2) JP-A No. 8-337749 (claims)
(Patent Document 3) JP-A No. 8-216498 (claims)
(Patent Document 4) JP-A No. 11-129460 (claims)
(Patent Document 5) JP-A No. 5-255623 (claims)